SEO and social media definitely work together. You have a product on your website, you write a cool blog post relevant to that product with unique content that people would enjoy reading or find useful, you share the blog post in your social networks, they read the blog post, hit the share buttons, go back to your website to check out the product, if not buy it, go back to their social networks telling everybody about the product, you engage with them, talk about the product, get feedback. It's a big circle. Search engines see all of this interaction and buzz, see the keywords being used, and give your pages a little bit of juice. Search engines definitely should, if they don't already, look at social buzz these days. It's a way to let users define authoritative sites and pages instead of just algorithms.